Many naturally occurring and man-made chemicals, such as phytoestrogens, organochlorine pesticides, polychlorinated biphenyls, dioxins, and synthetic estrogens, interfere with the endocrine system of vertebrates when released into the environment. Exposure to these compounds in the environment and in food poses serious risk to animal and human health by adversely affecting reproduction and development, and by promoting certain types of tumors. Using zebra fish embryos, this SBIR will develop a rapid, quantitative, high throughput assay for identifying endocrine disruptors. This SBIR will also assess compound effects on embryogenesis and patterning, including mortality and malformation. The zebra fish is uniquely suited for these assays; as a vertebrate, the zebra fish shares the molecular features of endocrine signaling with other vertebrates, including man, and has experimental advantages including transparency and rapid ex utero development. Zebra fish are also inexpensive to breed and maintain, and large numbers can be analyzed for statistically significant results.